1. Field of the Invention
The invention relates to real time computer systems having relatively low iteration rates for computer calculation updates. In particular, the invention relates to the provision of higher iteration update rates to the user system responsive to a computer, itself having relatively low update iteration rates.
2. Description of Prior Art
In real time dynamic computer systems, it is essential that the information used by the computer, to perform its calculations, be constantly updated. In digital systems this information is updated at iteration rates typically on the order of 15 to 30 cycles per second. If the information input to the computer is changing at high dynamic rates, a severe burden may be placed on the user system as it drives to react to the changed situation indicated each time the information is updated. For example, if the user system comprises highly responsive servomechanisms, a large change in the input could result in servo saturation. This could lead to lock-up or unwanted responses such as overshoot and ringing. Similarly, if the end-user system is a visual display presenting rapidly changing conditions, a noticeable stepping in the visual presentation (a glitch) may appear which is readily apparent to the eye of the observer.
It shall be a purpose of this invention to provide an interface between a computer having a low iteration update rate and user equipment responsive to the output of that computer, such that the interface provided by the invention allows the responsive system to be updated at a relatively high iteration rate. It shall be a further purpose of the invention to avoid the problems of unwanted system responses inherent in some systems as a result of large input step changes by updating the responsive system in least significant bit increments.
There are two methods generally employed in prior art to overcome the large step change which may occur in highly dynamic systems having low iteration update rates. The first of these is a value feedback system which feeds the derivative of the computer output to an integrator and uses the integrator's results to control the user system. For highest accuracy, it is necessary to close the loop back to the computer to verify the integrated results and adjust the derivative to the desired value. This system requires highly stable integrators and is operable only when the system is a direct function of the computer output or of a varying steady state condition. In a dynamic system in which the rate of change in value or phase must be adjusted, the value feedback system finds little or no application.
A better approach to solving the problem divides the period in which the information is updated into a fixed number of equal, incremental time segments. The new data values are then presented to the user system in incremental steps equal to the number of such time segments within the iteration period of the computer. A fixed clock is used to determine the equal incremental time segments. Although the system is superior, it still does not preclude data changes in larger-than-desired steps since there is no attempt to present the data at rates allowing least significant bit incrementation. The system also requires complex microcircuits, parallel multipliers and adders-substrators.
It shall be a further objective of this invention to provide data changes in least significant bit increments at a variable rate within the period at which data is normally updated to the system, while avoiding the complexity and the static time increments of the fixed clock system.